This first section from 2:4-4:26 concludes with an account of seven generations from Adam. Over the course of these generations, we see sin develop and expand alongside human culture. The city is invented. Nomadic animal husbandry and metallurgy are developed. Music is discovered. The generational line through Cain is as follows: Adam—Cain—Enoch—Irad—Mehujael—Methushael—Lamech. With Lamech we see the first mention of polygamy, and he also takes his ancestor’s bloodthirst further. If Cain’s offender would be judged sevenfold, Lamech claims to exact seventy-sevenfold revenge.
One of those interesting aspects that may be more novelty than message emerge here. Lamech is the seventh generation from Adam, so the writer gives us more details about his life. This is not just a coincidence of the story, but rather an important part of the literary structure of the passage. The writer is obsessed with sevens. If you create a database of all the Hebrew words used in Genesis so far, (and this is not an admission of any such endeavor) you discover a lot of sevenfold repetitions. The word Abel occurs seven times in Genesis. Cain fourteen times. In this section (2:4-4:26) we see Earth seven times and land fourteen. Even more astounding, God or LORD is used exactly 35 times in 2:4-4:26; and that corresponds with the 35 times in 1:1-2:3!
Finally, the writer tells us about Adam and Eve again, who have another son shortly after the death of Abel. They name him Seth, and he has a son who he names Enosh (Like Adam, another word for “man”). We see that, with Enosh, regular religious worship begins to be practiced. Where Abel and Cain tried to gain favor from God with a yearly or sporadic sacrifice, men now begin to hold regular worship services. Religion, just like sin, develops and expands. As man drifts further and further away from God, he tries to find ways to fill that void in his own power.